[en] Species living as epiphytes of marine macrophytes have often important role in ecosystem functioning, such as food web suppliers. Some animal or algae species may be considered as really specialised in the colonization of plant substrate and often dominates epiphytic community, particularly, on long life-span seagrass and macroalgae species. Because epiphytic compartment dysfunction is often implied in seagrass human-induced declining, it is important to understand dynamics and life traits of its specific component in pristine area. In our study, colonization dynamics, biomass seasonality, diet composition of Electra posidoniae, an epiphytic bryozoa, strictly found on the leaves of the seagrass Posidonia oceanica and dominating the leaf epifauna, were assessed monthly at 10 metre depth in the Revellata Bay (Corsica, Mediterranean sea). Aiming to delineate their trophic role in the ecosystem, we have performed bulk stable isotopes measurements and gut content analysis.